Dot printing apparatus

ABSTRACT

Wire matrix dot printing apparatus is disclosed in which a plurality of wire impact members are driven by electromagnetic means arranged in a circular pattern at the rear of a wire matrix print head. The wires are caused to converge following the arc of free bending in the wire from the circular array at the driver end to a parallel and colinear alignment at the printing or output end of the print head. The individual wires are continuously guided from the end where the drivers are located to a point where they are nearly parallel and colinear by utilizing an improved two-piece wire guide consisting of an inner cone with grooves on its surface and an outer shell which confines the wires to the grooves in the inner cone. The shape of the inner cone is such that the paths of the wires converge from a circular array at the driver end of the print head to a nearly colinear and parallel array at the output end of the print head.

United States Patent mi Darwin et al.

l l DOT PRINTING APPARATUS [22] Filed: Dec. 11. I973 [2]] Appl. No: 423.833

[73] Assignee:

[52] U.S. Cl. 197M R; l()lf93.05

[51] int. Cl. B4Ll 3/05 [58] Field Of Search 197, '1 R; l(ll.l )3.(l4 93,05

{56] References Cited UNlTED S lA l ES PATENIS Z,IZ9.U(15 9/1938 Loop lf fl R 3,333 667 M1967 Nordin. 197M R 1 467.23 H1969 Paige. WW1 R 3 845? 6/1971 Distl 197M X 3 591.3ll 7, l97l Chou et alv lfill R 3 617.096 l2ll97l Finnegan... liT/l R 3.672.482 (H1972 Brumhaugh ct al. 197M R 3.69U -'l3| H1972 Howard,........ [97H R 451 Aug. 5, 1975 Primary li.\rmn'ncrj. Reed Fisher Assixlrln! l; .\umiuerR. T. Radcr niHUIHL). Agent. or FirmEdw-ard H. Duffield 5 7] ABSTRACT Wire matrix dot printing apparatus is disclosed in which a plurality of wire impact members are driven by electromagnetic means arranged in a circular pattern at the rear ofa wire matrix print head. The wires are caused to converge following the arc of free bending in the wire from the circular array at the driver end to a parallel and colinear alignment at the printing or output end of the print head. The individual wires are continuously guided from the end where the drivers are located to a point where they are nearly parallel and colinear by utilizing an improved two-piece wire guide consisting of an inner cone with grooves on its surface and an outer shell which confines the wires to the grooves in the inner cone. The shape of the inner cone is such that the paths of the wires converge from a circular array at the driver end of the print head to a nearly colinear and parallel array at the output end of the print head.

7 Claims, 10 Drawing Figures 51975 PATENTEUMJE SHEET 1 SHEET PATENTED RUB 51975 DOT PRINTING APPARATUS FIELD OF THE INVENTION This invention relates generally to printing apparatus of the matrix or composite printing type and more specifically to the dot matrix printing apparatus of the flex ible wire type.

BACKGROUND AND PRIOR ART Wire matrix print heads are generally wellknown and have been provided in a variety of previous de signs. Notably, the Preisinger US. Pat. No. 3,108,534, assigned to the Assignee of the present invention. teaches an early form of wire matrix print heads in which a plurality of print wires were constrained and aligned by guides to form a straight line at the output or printing end of the head while the drivers were ar ranged in a fan array at the opposite end of the wires. Similarly, the Distl US. Pat. No. 3,584,575 illustrates a printing head of the wire matrix type in which the guide channels for the printing wires extend between electromagnetic drivers and a mouthpiece on a curved path which corresponds to the free bending line of the printing wires; however, in the mouthpiece itself, the curve departs from the free bending curve to angled converging channels which bring the wires together so that, in the extended position, the wires form a straight line when they are forced to extend from the mouthpiece by the electromagnetic drivers. The drivers in the Distl patent are arranged in a fan array and hence the path length of each wire is slightly different. This leads to a condition of excessive wear on the outer or most curved wires.

Somewhat similar and related designs are shown in US. Pat. Nos. 3,627,096 to Finnegan and 3,592,311 to Chou et al. In these latter patents, the fan array of wires and drivers was utilized together with a solid guiding member or block containing grooves to confine the wires to the appropriate paths. In these designs, the outermost wires in the array must follow a more curved or confined path than the inner members and the path lengths are not equal.

One approach to solving the problems created by un equal path lengths and unequal bending in the wires is shown in the Paige US. Pat. No., 3,467,232 in which the wires are arranged in a conical array with the drivers in a circular pattern at one end of the print head and the wires converging in straight lines to a nose piece or mouthpiece which alters the paths slightly to cause the wires to converge to a straight line position when they are in their extended position for printing. This design created equal path lengths, free of bending, but did not create a parallel or nearly parallel alignment of the wires prior to exit from the head. The parallel alignment of the wires prior to extension from the head is a desirable characteristic but is difficult to achieve in these types of designs in which path lengths are equal. Parallelism of the wires and continuous guiding of them from the driver end to the output end is most desirable so that deflections in the extended wires will not occur to an undue extent and create erratic print lines. Undue interference between wires actually touching or colliding, as is the case with the convergent designs, in which the wires finally converge to a straight line only in their extended position, is also desirably avoided.

Similarly, the use of solenoids or other similar electromagnetic devices to drive wires is well-known as is shown in US. Pat. No. 3,690,431 and the aforementioned Paige, Chou, Finnegan and Distl patents. Magnetostrictive devices for moving print wire have also been used as shown in US. Pat. No. 3,103,534 mentioned previously.

The primary disadvantages of these previous known designs are that they either produce an unequal path length in the wires, with the coincident unequal bending even though the bending may approximate the free bending curve of a wire, or the designs fail to create parallelism among the various wires at the output end until they are extended to protrude from the print head in an unsupported fashion to impact the printing medium. The difficulties with these designs are that unequal path lengths and unequal bending in the wires lead to premature failure in the most highly stressed or most severely bent wires or impact members. Similarly, the convergent style print heads. in which the wires converge to a line only when they protrude from the print head itself, create difficulties in maintaining good print quality since interference between the converging wires and the fact that they are relatively unsupported until they converge leads to slight deflections and motions which may produce slight defects in the actual printed material.

It is also most desirable that a continuous support or guide be provided for the individual wires or print members and, while this has been provided to a very great extent in the aforementioned Chou, Finnegan and Distl patents, the method of forming the guides of one piece of material is technically difficult since a mold with inserts to create the channels must be made up, the guide material flowed around wires or mold members and then hardened, and then the inserts must be withdrawn leaving channels for the wires, as is de scribed in the Distl patent. This is a tedious method of constructing the print heads and leads to high cost and low yield because of defects in the casting process. Additionally, these designs, while providing nearly continuous support for the print members from input to output, generally incur unequal path lengths and unequal bending in the various members with the accompanying problems previously noted.

OBJECTS OF THE INVENTION In view of the foregoing difficulties and shortcomings with the known prior art devices of this type, it is an object of the present invention to provide an improved wire matrix print head having continuous guide support for the individual wires or print members from the input to the point at which they are parallel and nearly colinear at the output end.

It is a further object of this invention to provide an improved guide means for the individual print members which is of simpler and easier construction than that known in the prior art and which is uncomplicated to assemble.

Another object of this invention is to provide an improved wire matrix print head in which the paths of the individual wires or print members are equal, have equal bending, and are parallel at the output instead of com vergent.

SUMMARY OF THE INVENTION The foregoing and other objects of the invention are met by utilizing a unique, two-piece wire guide in which an inner, grooved, generally conical-shaped member is surrounded by a mating outer shell which confines the individual print members to the grooves. At the driving (or driven) end, the wires are arrayed in a circle for ease and convenience of attaching, as compactly as possible, a plurality of wire drivers of an electromagnetic type. From the point where the drivers are at tached to the wires. the wires converge along generally concave surfaces to the point where they are parallel and are nearly in the same plane. At this point. it becomes impractical to continue the inner cone further because the thickness of guiding material is reduced nearly to the vanishing point. An outer shell is provided which matches the contours of the inner cone and confines the individual wires or print members to the grooves in the cone. At the exit end of the guide. the wires are parallel and lie nearly in a straight line. being slightly staggered left and right of vertical as viewed end-on. A short unsupported area follows after which the wires are brought into final linear alignment by a simple guide shoe which brings the parallel wires together in a straight vertical line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I illustrates a partial cross-sectional view, approximately full size, of the improved wire matrix print head of the present invention.

FIG. 2 illustrates a view of the print head shown in FIG. 1 taken from the left (rear) of the print head.

FIGS. 30 and 3/) illustrate views of the print head taken from the right. or output. end of the print head shown in FIG. 1.

FIGS. 414C illustrate schematically the general form and geometrical requirements of the inner cone and outer shell utilized in the present invention.

FIG. illustrates an enlarged partial cross-section of part of FIG. 1.

FIGS. 6a and 6b illustrate the attachment ofthe wires to the armatures. in enlarged partial cross-sectional views.

Turning now to FIG. 1. a preferred embodiment of the invention will be described. As illustrated in FIG. 1, the overall print head I is a generally conical shaped structure. Head 1 is made of. for example. injection molded plastic such as a material commercially avail able under the trade name Nylaglass and produced by the Fiberfil Corporation. Other suitable plastic materials would be any of the well-known nylons, flurocarbons, and various filled composition plastics, but metals could also be utilized to advantage; the choice being one mainly of cost and ease of manufacture. Print head I is basically a two-part construction comprising a wire guide 2 and a driver head assembly 3. The wire guide assembly 2 consists of an outer cone or shell 31 visible in FIG. I, and an inner cone 28 with grooves in it to guide the wires which is shown in FIG. 4. A plurality of individual wires 4 are disposed in a circular array at the driver end 3 of the print head I. The circular array of drivers may be seen to advantage in FIG. 2. Each individual wire 4 passes through an aperture 5 in an indi vidual fixed pole piece 6 and ends in a movable armature 7 where it is attached in place in a manner described later. Armature 7 is made of soft iron or other suitable electromagnetic material exhibiting high magnetism. The armature 7 and pole piece 6 are disposed in the aperture of an annular electromagnetic coil 8 which is wound about a bobbin 9, the hollow inner portion of which forms the core or working gap of the electromagnetic driver system in which the armature 7 and the pole piece 6 are disposed as noted. As shown clearly in FIG. 5. compression return spring 10 is mounted in a recess or counterbore ll, of the fixed pole piece 6. Spring 10 abuts against the armature 7. For clarity. the spring 10 and recess ll are not shown in FIG. I. The compression spring 10 is under compression as assembled and the pole piece 6 is held in place in element 17 under force fit or by uti izing a screw or friction fit. not shown. Armature 7 has a clearance which allows it to slide freely in the inner core of bobbin 9. Under the impetus of return spring 10. armature 7 is forced to the left to the position illustrated in FIG. 1, thereby drawing wire 4 back into its unextended position at the output end 12 of print head I. The movable armature 7 is held in place by a backstop l3 made of non-magnetic material which is preferably sintered tungsten carbide or another hard material to reduce wear between the abutting surfaces of armature 7 and backstop [3. Each backstop I3 is held resiliently in place by a lobe of a multi-lobed leaf spring 14. Spring 14 is clamped to the rear of the driver portion 3 of head 1 by a screw 15 and a plate 16 which act as a clamp to hold leaf spring 14in compression to maintain backstops 13 as well as magnetic pieces 7, l7, and 18 in position under about 10 lbs. of spring pressure.

Backstop l3 rests on a portion of a C-shaped magnetic return circuit made up of an L-shaped piece 17 of soft iron or similar highly magnetic material. and a straight portion 18 abutting the L-shaped portion to form a general C-shape as shown. Portion I8 is also of ferromagnetic material and has an aperture in which an extension of the core of bobbin 9 is centered and within which resides movable armature 7. Electromagnetic coil 8 may suitably be made of 230 turns of No. gauge copper magnet grade wire which may be driven by a current source of approximately 3.5 amperes at 24 volts for 375 microseconds, not shown. This provides sufficient magnetic attraction between the coil 8 and the armature 7 to overcome the compression of spring 10 and allow armature 7 to move to the right until it abuts fixed pole piece 6 and causes the individual wire 4 to protrude from the head 1. Circuit board carries the coil lead connections for coils 8 together with the usual diode suppressors. The individual parts making up the driver portion 3 of head 1 are suitably mounted on a formed plastic chassis 19 which is actually a flanged portion of the back of inner core member 28 of guide 2. This can be seen to advantage in FIG. 4.

The resulting structure is of quite low mass, as will be readily appreciated, and is thus an easily movable print head assembly which may be utilized in a variety of printer mechanisms and which will require little power to move it along a line of print if movable print head operation is desired. The salutory effects achieved in movable print head designs by the use of very low mass print heads will be readily appreciated by those of skill in the art.

Individual print wires 4 are suitably made of Tungsten Carbide and have a diameter of approximately 0.011 inches so that they are quite flexible and easily conformed to the free bending path to be defined below. Spring 21 is of the wavy spring washer type. It is used to locate the bobbin 9 against the surface of 18 toward which it will be pulled when the coil 8 is energized. Spring 21 insures that coil 8 and bobbin 9 will be held tightly against the C-shaped magnetic return elements 18 previously discussed.

Turning to FIG. 2, a rear or left side view as shown in FIG. 1 of print head 1 is illustrated. In FIG. 2, the circular array formed by non-magnetic backstop members 13 is clearly visible and the multilobed leaf spring 14 together with clamping plate 16 and screw 15 are visible. In FIG. 2 eight symmetrically displaced backstops 13 corresponding to eight symmetrically disposed driver assemblies are shown. Eight individual print wires 4 are contemplated as a preferred embodiment. although it is well-known that the number of wires utilized may be adjusted and varied to suit different printing fonts or criteria as desired. The entire assembly of members l3,18 and 17, 17 not being visible in FIG. 2, is held in place by leaf spring 14 which is clamped by plate 16 and by screw 15 as it is better seen in FIG. 1. The individual Lshaped members of the magnetic return circuit 17 are held in place on flange 19 by spring pressure of about 10 lbs. from spring 14.

Turning to FIG. 3a, a sectional view of the output end of the wires 4 as they emerge from guide 2 is shown. It may be seen that the ends of the wires are parallel as they emerge from the guide, but do not lie in a vertical linear array since they are slightly staggered left and right of vertical. As shown in FIG. 3b, a simple array of holes in the guide shoe portion 24 affixed to the end of guide 2 (shown in FIG. 1) aligns the wires into a vertical line.

Because the individual wires 4 which emerge from guide 2 are parallel, there are no severe bending stresses in the unsupported portion of the wires between the end of the guide 2 and the alignment tip 24 to cause the wires to depart from parallel array nor to converge and wear unduly by touching and interacting with one another. Lubrication may conveniently be applied to the individual wires 4 by providing an aperture in nose piece 24 illustrated in FIG. 1 as aperture 25 in which a lubricant saturated material may be inserted and brought into contact with the exposed portion of the wires in aperture 26. The lubricant material is not shown for the purpose of simplicity, but may be a simple felt wick or some more sophisticated design, as de sired.

On assembly, guide 2 with the nose portion 24 having the final alignment tip in it, is mounted together with shell 31 via means of screws to the core 28. Circuit board 35 is clamped between shell 31 and the flange 19 of core 28 as shown. The Lshaped pieces of magnetic return circuit, elements 17, are then inserted and held in place with the fixed pole pieces 6 inserted in them. Next, springs 21 are inserted over the pole pieces 6 and bobbins 9 containing the coils 8 are slid into place. As shown in FIG. 5, individual armatures 7 having wires 4 brazed in brass ferrules 33 which are embedded in plas tic 34 in recesses in armatures 7 to hold wires 4 in place are then provided with return spring 10 and are dropped into position with the wires extending through apertures 5 in the pole pieces 6 and on through the guide assembly 2 to the output, or nose portion 24. The return circuit completing pieces 18 are then set in place and retaining backstops 13 are placed over the pieces 18. The backstop members 13, affixed by a tab 27 to leaf spring 14, are clamped in place by a clamp plate 16 and screw 15, thereby completing the mechanical assembly of the print head. The individual wires 4, which protrude in the initially assembled state due to being provided at a slightly greater length than necessary, are then ground off flush with one another to approximately 0.003 inches protrusion from nose piece 24, thereby completing the manufacturing operation of the print head.

Turning now to FIGS. 4a4c, a schematic view of a typical inner cone 28 is shown together with outer mating shell 31. Although the inner core 28 is described generally as conical, it will be appreciated that the surface depicted departs from a true conical shape in several respects, but for simplicitie's sake is referred to as essentially conical. The surface of the inner guide piece 28 can be described geometrically as being formed by joining a circle in one plane with a straight line in another parallel and spaced plane by utilizing numerous circular arc segments to define a generally concave sur' face which has a circle at one end and a straight line at the other. The actual inner member 28 which results is somewhat more difficult to depict graphically, but it starts from a circular face 29 and follows generally con cave surfaces having grooves 30 to the exit point on the end surface where the individual grooves are parallel and are nearly colinear as seen in FIG. 40. As may be seen, the arcuate line segments defining a concave sur face do not converge to a straight line, but to a slim, generally rectangular shape at which it becomes impractical to continue the guide surface any further. The inner member 28 is made of molded plastic and the grooves 30 are molded in place. Except for a slight amount of material on each side of the grooves 30, the remaining plastic material of inner member 28 may be removed or, by proper construction of the original mold, left out for weight savings and cost reduction as illustrated. The individual grooves 30 are then seen to be on the concave surface formed by line segments at the top of what will be individual ribs emanating from the central portion of the core 28, but this refinement in technique and design of the construction does not alter the basic path of the wires or the geometrical construction described. The arcuate segments required to build up the generally concave surface elements are the arcs described by the free bending path of individual wires of the length required to traverse the distance from the driver end at the circular array to the final output end of the print head previously discussed. The shorter the wires, it may be seen, the sharper will be the bending radius for a given placement of wire drivers. In the preferred embodiment, the individual wires are approximately 3 inches long and the diameter of the circular array at the driving end is approximately 2% inches at the end of the wires. The length of the small rectangle to which the wires converge along their concave path is approximately one-tenth inches which is the height of the printed characters which may be produced on the printing medium using individual wires of 0.011 inches diameter and eight in number.

The outer shell member 31 can have an outer surface shape of any desired form, but to conserve material, it is generally conical shaped as shown. It may, as is obvious, carry the grooves 30 instead of having them on the core 28. Its interior surface is molded to match the exterior surfaces and contours of the inner member 28.

The chassis support 19 for the driver end 3 is preferably molded as a portion or extension of the inner member 28 as illustrated in FIGS. 4b-4c. This simplifies the construction and provides a portion to which fastening screws 20 can be inserted to hold the outer shell elemerit 31 in place as illustrated in FIGS. 1 and 4b and locates the solenoids properly with respect to the grooves 30.

As will be readily appreciated by those skilled in the art. the improved printing head apparatus described is equally useful in both moving print head and fixed print head designs. Similarly. the ease of manufacture of the print head, which utilizes basically only two molded plastic parts for the guide means, is greatly improved. The improved wire matrix print head. by utilizing wires of nearly equal length, equal bending and a continuous guide surface from the input end to the point where the wires are aligned and parallel. will be readily appreciated as a step forward to those skilled in the art. The inherent simplicity of construction and design plus equalization of stresses makes for a long useful life for the subject print head.

In addition, the use of molded plastic guides of twopiece construction as described and the elimination of many separate guiding parts reduces the overall size and mass of the printing head. For example, printing heads constructed according to the teachings of this specification and utilizing eight printing elements have been built and tested to work perfectly in excess of 300 X wire drives for each wire. These printing heads have been approximately 4 inches long, 2% inches in diameter at the circular end. and produce parallel aligned printing elements having a bend radius of approximately 6 inches each. Total mass of such a head is approximately 210 grams.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.

What is claimed is:

l. Dot printing head apparatus, comprising:

a plurality of elongated, flexible, axially extendable, double-ended. printing elements. each having an impact surface upon one end thereof;

a supporting means for supporting said printing elements. said supporting means having a continuous solid geometrical surface;

said surface of said supporting means being generally concave and varying continuously in crosssectional form from an approximate circle to an approximate rectangle, with said rectangle being approximately as wide as the cross-sectional dimension of one of said printing elements and as long as the combined cross-sectional dimensions of said printing elements;

guide means for confining said printing elements to lie on said geometrical surface; and

means connected to the ends opposite said impact surfaced ends of said printing elements for extending said elements.

2. Apparatus as described in claim I, wherein:

said guide means comprises an inner member defining said geometrical surface of said supporting means and an outer shell member for confining said printing elements to lie in said geometrical surface.

3. Apparatus as described in claim 2, wherein:

said inner member defining said geometrical surface has grooves on its outer surface for confining said printing elements to lie on said geometrical surface and be retained by said mating outer shell member in position.

4. Apparatus as described in claim 2, wherein said outer shell member has grooves on its inner surface for confining said printing elements to lie in said grooves and on said geometrical surface defined by said inner member.

5. Apparatus as described in claim 2, wherein:

said print elements are parallel to one another at said portion of said guide means which is approximately rectangular in cross-sectional shape.

6. Apparatus as described in claim 5, wherein;

said inner member is a shaped geometrical solid ap proximately defined by a circle in a first horizontal plane. said circle being connected to a line lying in a second horizontal plane parallel to said first plane, said connection being by means of a plural ity of arcuate line segments arrayed so as to form a generally concave exterior surface of said shaped geometrical solid.

7. Apparatus as described in claim 6, wherein:

said arcuate line segments are taken from a circle defined by the free bending line of one of said printing elements. 

1. Dot printing head apparatus, comprising: a plurality of elongated, flexible, axially extendable, doubleended, printing elements, each having an impact surface upon one end thereof; a supporting means for supporting said printing elements, said supporting means having a continuous solid geometrical surface; said surface of said supporting means being generally concave and varying continuously in cross-sectional form from an approximate circle to an approximate rectangle, with said rectangle being approximately as wide as the cross-sectional dimension of one of said printing elements and as long as the combined cross-sectional dimensions of said printing elements; guide means for confining said printing elements to lie on said geometrical surface; and means connected to the ends opposite said impact surfaced ends of said printing elements for extending said elements.
 2. Apparatus as described in claim 1, wherein: said guide means comprises an inner member defining said geometrical surface of said supporting means and an outer shell member for confining said printing elements to lie in said geometrical surface.
 3. Apparatus as described in claim 2, wherein: said inner member defining said geometrical surface has grooves on its outer surface for confining said printing elements to lie on said geometrical surface and be retained by said mating outer shell member in position.
 4. Apparatus as described in claim 2, wherein said outer shell member has grooves on its inner surface for confining said printing elements to lie in said grooves and on said geometrical surface defined by said inner member.
 5. Apparatus as described in claim 2, wherein: said print elements are parallel to one another at said portion of said guide means which is approximately rectangular in cross-sectional shape.
 6. Apparatus as described in claim 5, wherein: said inner member is a shaped geometrical solid approximately defined by a circle in a first horizontal plane, said circle being connected to a line lying in a second horizontal plane parallel to said first plane, said connection being by means of a plurality of arcuate line segments arrayed so as to form a generally concave exterior surface of said shaped geometrical solid.
 7. Apparatus as described in claim 6, wherein: said arcuate line segments are taken from a circle defined by the free bending line of one of said printing elements. 